Electrical fuses (eFuses) are used in the semiconductor industry to implement array redundancy, field programmable arrays, analog component trimming circuits, and chip identification circuits. Once programmed, the programmed state of an electrical fuse does not revert to the original state on its own, that is, the programmed state of the fuse is not reversible. For this reason, electrical fuses are called One-Time-Programmable (OTP) memory elements.
The mechanism for programming an electrical fuse is electromigration of a metal semiconductor alloy induced by an applied electrical field and a raised temperature on a portion of the electrical fuse structure. The metal semiconductor alloy is electromigrated under these conditions from the portion of the electrical fuse structure, thereby increasing the resistance of the electrical fuse structure. The rate and extent of electromigration during programming of an electrical fuse is dependent on the temperature and the current density at the electromigrated portion.
For scaling of electrical fuses, it is necessary to reduce the size of a programming transistor that applies a programming current to the electrical fuses. However, reliable programming of electrical fuses requires at least a minimum current density above which electromigration of the metal semiconductor alloy is induced. Therefore, it is advantageous to form a portion having a narrow with in an electrical fuse structure.
Dimensions of semiconductor structure are typically limited by a minimum printable dimension of a lithography tool employed to pattern the physical feature of the semiconductor structure. The minimum printable dimension is measured by a critical dimension of the lithography tool, which is defined as the width of narrowest parallel lines or narrowest parallel spaces having a minimum pintable pitch. Thus, a typical electrical fuse has a “fuselink” at which the width of the electrical fuse is a critical dimension, or a “lithographic minimum width” for a given lithography tool. The size of a programming transistor is designed to deliver at least the minimum current density to the fuselink.
While a “lithographic minimum dimension” and a “sublithographic dimension” are defined only in relation to a lithography tool and normally changes from generation to generation of semiconductor technology, it is understood that the lithographic minimum dimension and the sublithographic dimension are to be defined in relation to the best performance of lithography tools available at the time of semiconductor manufacturing. As of 2007, the lithographic minimum dimension is about 50 nm and is expected to shrink in the future.
An electrical fuse having a sublithographic width in the path of the programming current would provide a higher current density for a given programming current than an electrical use having a fuselink with a lithographic minimum width. Thus, less programming current would be necessary to program the electrical fuse having a sublithographic width, and a smaller programming transistor would be required for programming of the electrical fuse.
In view of the above, there exists a need to provide an electrical fuse structure having a sublithographic dimension and methods of manufacturing the same.
Further, most semiconductor circuits require passive components such as resistors. The resistance of a resistor is determined by the resistivity of the material comprising the resistor and the length, width, and the height of the resistor. While formation of a resistor having a sublithographic height may be effected by controlling the thickness of a layer comprising the resistor, formation of sublithographic dimensions in the length and/or the width of a resistor are difficult to achieve.
Therefore, there also exists a need to provide a resistor structure having a sublithographic dimension and methods of manufacturing the same.